A humidifier is a device for supplying breathable air to user. An air inlet of the humidifier communicates with a blower and an air outlet of the humidifier communicates with a breathing mask. Air from the blower is humidified in the humidifier and then passes to the breathing mask through an air delivery conduit. The humidifier generally includes a first cover, a second cover and a partition plate. The first cover defines the air inlet for air to enter and the air outlet for air to flow out. The second cover includes a chamber with some water. A heating plate is embedded in a bottom of the chamber to heat the water to generate humidified air. The air from the air inlet is humidified by mixing with the humidified air and passes out of the humidifier through the air outlet. The partition plate is located between the first cover and the second cover to prevent the water from entering the air inlet or the air outlet of the first cover. Traditionally, the partition plate is just a flat plate for preventing water in the second cover from entering the air inlet and the air outlet in the first cover. However, when air flows into the humidifier through the air inlet, a resonance phenomenon will occur in the single chamber of the humidifier and noise is thus generated. The noise generated from the resonance can be a disturbance to a user either awake or asleep. In addition, prior humidifiers did not provide flow with high humidity and thus it was uncomfortable for a user to breathe the air generated.